This invention relates to a trace element spectrometer with plasma source (simply referred to as a plasma trace element spectrometer hereinafter) such as plasma source mass spectrometer or plasma emission spectrometer used for quantitative analysis of trace elements in the field of biology and the like, and more particularly to a means of plasma production using microwave power suitable for improving excitation efficiency for samples in this type of spectrometer.
Conventionally, there have been available two types of plasma production means in the plasma trace element spectrometer, one type using RF power at 27 MHz (for example, Philips Tech. Rev., Vol. 33, No. 2 (1973), pp. 50-59: literature 1) and the other using microwave power at 2.45 GHz. The apparatus utilizing microwave power is further classified into two types: one uses a microwave cavity with TM.sub.010 mode (for example, Applied Spectroscopy, Vol. 39, No. 2 (1985), pp. 214-222: literature 2) and the other is based on a surface wave excitation with capacitive coupling method and called "Surfatron" (for example, Spectrochimica Acta, Vol. 37B, No. 7 (1982), pp. 583-592: literature 3).
Of the above prior arts, the RF excitation method disclosed in literature 1 can provide a radial distribution of plasma parameters (such as temperature and density), which is ideal for the trace element spectrometer but it leads to disadvantages of large-sized and expensive apparatus, low ionization efficiency and complexity in adjustment. On the contrary, the microwave excitation method of literatures 2 and 3 can eliminate the problems encountered in literature 1 but suffers from disadvantages of degraded characteristics of radial distribution of the plasma parameters, low introduction efficiency for samples non-uniformity in heating and ionization of the sample particles and low measurement sensitivity.